Halocarbons containing chlorine or bromine, in particular chlorofluorocarbons or bromofluorocarbons, have been widely used as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing agents, and power cycle working fluids. Many of these chlorofluorocarbons and bromofluorocarbons are considered to be detrimental toward the Earth's ozone layer. The worldwide effort to develop materials having lower ozone depletion potential has identified numerous hydrofluorocarbons (i.e. compounds containing only carbon, hydrogen and fluorine) which can serve as effective replacements for chlorofluorocarbons or bromofluorocarbons in the applications listed above. For example, the hydrofluorocarbon 1,1,1,2-tetrafluoroethane (HFC-134a) is being used as a replacement for dichlorodifluoromethane (CFC-12) in refrigeration systems. Another hydrofluorocarbon, 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), has been identified as a promising replacement for chlorofluorocarbons or bromofluorocarbons in several applications.
The production of hydrofluorocarbons has been the subject of considerable interest in order to provide environmentally desirable chlorofluorocarbon and bromofluorocarbon alternatives to the market place. The reaction of hydrogen fluoride (HF) and hexafluoropropylene (HFP) is known in the art. However, the highly exothermic reaction requires significant cooling of the reaction zone to prevent overheating of the catalyst. This excess heat can be responsible for the production of undesirable by-products and reduced catalyst lifetime.
The products of the reaction of HF and HFP include HFC-227ea as well as excess HF and HFP. The excess HFP and the other organic impurities can be removed by conventional separation techniques. But recovery of the unreacted HF is difficult due to the formation of a low-boiling azeotrope of HFC-227ea and HF.
It is the object of this invention to provide a process for the production of HFC-227ea which recovers and recycles the excess HF as the azeotropic composition of HF and HFC-227ea and circulates the excess HFC-227ea as a diluent in the system to control the temperature rise in the reaction zone.